1. Field of the Invention
The invention relates to an electronic brake system for road vehicles with an electronic device furnishing a control of brake pressure modulators, where the electronic device includes several wheel modules and a central module based on a microprocessor.
2. Brief Description of the Background of the Invention Including Prior Art
Such an electronic brake system is known from the German Printed Patent Document DE-A 2,622,746. A brake value given by a driver by way of a transmitter is represented as an electronic voltage value in such electronic braking systems. This voltage can then still be further modified in an electronic device. For example, a desired characterizing curve between the brake pedal position and the generated brake force can be reconstructed in this way. Furthermore, it is possible to take into consideration the load of the vehicle with an automatic load-sensing brake, or to furnish an antilock protection by including an antilock braking system. The thus modified voltage is then amplified and is fed to solenoid valves coordinated to the individual wheels. The pressure agent, which can act hydraulically or by compressed air, is automatically controlled by the solenoid valves actuating the individual brake.
The German Printed Patent Document Laid-Open DE-OS 3,841,750-A1 to Erwin Petersen et al. teaches a process and arrangement for an electrically controlled brake circuit of a multi-circuit brake system where the brake value is measured by a brake circuit controlled by a pressure signal and is transformed into an electrical brake value signal, and wherein the electrically controlled brake circuit is controlled, respectively co-controlled by this brake value signal under normal operating conditions.
The German Printed Patent Document Laid-Open DE-OS 3,829,951-A1 to Bernhard Toepfer et al. teaches a method for a load-dependent control of the brake pressure at vehicles and a device for performing the method. Only wheel rotation speed differences are used as actual values of an electronic brake pressure regulator and axial load sensors are dispensed with.
The German Printed Patent Laid-Open DE-OS 3,502,049-A1 to Erich Reinecke teaches a brake pressure control device. The reference proposes to sense wheel brakes relative to their brake force and their wheel braking temperature for balancing the wheel brakes.
The German Printed Patent Laid-Open DE-OS 3,313,078-A1 to Egbert Muller et al. teaches a brake-pressure regulator. Sensors are employed for determining a residual lining thickness and the output signals are fed to a central control electronics.
The U.S. Pat. No. 3,545,817 to Gordon W. Yarber teaches a brake control mechanism where a command pressure for the entire vehicle is modified in accordance with a measured function of road friction, typically derived from vehicle deceleration.
The U.S. Pat. No. 4,850,650 to Steve J. Eckert et al. teaches hierarchical brake controller with a high level supervisory controller and a low local controller, where the supervisory controller receives a vehicle deceleration rate command from the vehicle operator. The supervisory controller proportions the commanded brake line pressure between the front and rear brakes. The local controller at each wheel limits the applied brake pressure in response to a sensed incipient wheel lockup condition.
The U.S. Pat. No. 4,749,238 to William A. Singleton et al. teaches an electronically controlled fluid pressure braking system including an operator controlled mechanism which generates independent brake pressure command signals, each of which are transmitted to separate auxiliary controllers. Each of the auxiliary controllers is capable of generating a brake pressure request signal independent by of the master control unit if a control signal is not within normal limits.
A main advantage of an electronic brake system, taught in the German Printed Patent Document DE-A-2,622,746, as compared to a conventional braking system, where the actuating variable is led from a pneumatic brake valve to the brake cylinders in case of a compressed air brake system in commercial vehicles, is associated with increased speed and the possibilities of easy modification of the electric actuating variable.
Special emphasis is placed on the safety of the system and on low costs in the application of an electronic brake system in commercial vehicles. Furthermore, an error should be easily localized and pinpointed in case of defects in the electronic device and a defect should be correctable by a simple exchange of components or otherwise.
Conventional concepts of electronic brake systems are based on a centrally constructed brake system, i.e. a centrally disposed control unit determines all information necessary for the braking, such as the position of the braking pedal, the braking pressure, the braking torque, the rotation speed of the wheels, etc. The reference values for the brakes are obtained from this information and the corresponding actuators are triggered. Additional tasks of the central control unit include essentially the monitoring of the complete braking system, the display of the operating state of the braking system, and the initiation of correction measures in case of defects and errors.
Furthermore, a vehicle electronic device is known from the German Printed Patent Document DE-A 3,335,932, which is subdivided into several function modules, such as, for example, for climate control, for antilock protection, etc. The modules include microprocessors, which perform their tasks according to a predefined program, and thus these microprocessors provide intelligence to the system. These modules are disposed at a central location in the vehicle and can be easily individually exchanged in case of disturbances.
The modules are connected to several so-called subdivisions via a multiplex sender/receiver. These subdivisions are disposed decentralized in the corners of the vehicle, they decode the multiplex signals and they transfer the commands of the central module to connected device components such as lamps, actuators, or valves. Furthermore, a feedback signalling to the central module such as, for example, of signals of connected sensors is possible
Even though the subdivisions also include a microprocessor, they are not associated with their own intelligence as taught in the German Printed Patent Document DE A 3,335,932 rather they deliver only commands and measurement values, respectively, via the multiplex system.
The conventional systems with intelligence centrally disposed in the vehicle, i.e., the central electronic device with microprocessors, are associated with certain disadvantages. For example, the electric lines from the electronic device to the actuators and from the sensors to the electronic device are relatively long and therefore subject to interferences and disturbances. If currents of too high a value are flowing, then these lines furnish furthermore a source of disturbance. Furthermore, the central electronic device is constructed very complex, based on the large number of sensors and actuators. The sensitivity and interferences are further increased by said complex construction as well as by the large number of lines and plug connections. In addition, part systems, such as, for example, solenoid valves, cannot be exchanged without further consideration with other models, since the software of the central electronic device is adapted to the specification data of the valves, in particular to their switching times.